Extract translation partial to be shared within admin

Refactor: behaviour should be 100% the same

config/locales/en/admin.yml

@@ -269,8 +269,6 @@ en:
         show_image: "Show image"
         documents: "Documents"
       form:
-        add_language: Add language
-        remove_language: Remove language
         admin_statuses: Admin investment statuses
         no_statuses_defined: There are no defined investment statuses yet
       new:
@@ -1377,3 +1375,6 @@ en:
         submit_header: Save header
         card_title: Edit card
         submit_card: Save card
+    translations:
+        remove_language: Remove language
+        add_language: Add language

config/locales/es/admin.yml

@@ -270,8 +270,6 @@ es:
         show_image: "Mostrar imagen"
         documents: "Documentos"
       form:
-        add_language: Añadir idioma
-        remove_language: Eliminar idioma
         admin_statuses: Gestionar estados de proyectos
         no_statuses_defined: No hay estados definidos
       new:
@@ -1378,3 +1376,6 @@ es:
         submit_header: Guardar encabezado
         card_title: Editar tarjeta
         submit_card: Guardar tarjeta
+    translations:
+      add_language: Añadir idioma
+      remove_language: Eliminar idioma